Low-pour dewaxing process utilizing dual solvents

ABSTRACT

An improved process for dewaxing petroleum oil stocks. A dual solvent consisting of an autorefrigerant and a wax antisolvent is employed to chill the petroleum oil and precipitate out the wax. The autorefrigerant is used to strip the wax antisolvent from both the precipitated wax and the dewaxed oil and may be used additionally as blow gas for the filters.

United States Patent [72] lnventors Frank A. Biribauer Cranford; James D. Bushnell, Berkeley Heights; Richard E. Winsor, Fanwood, all of NJ. Appl. No. 882,025 Filed Dec. 4, 1969 Patented Nov. 23, 1971 Assignee Esso Research and Engineering Company LOW-POUR DEWAXINC PROCESS UTILIZING DUAL SOLVENTS 12 Claims, 1 Drawing Fig.

Int. (I Clg 43/08 Fleld 01 Search 208/33, 35

References Cited UNITED STATES PATENTS Primary Examiner-Herbert Levine Atlomeys- Pearlman and Stahl and N. Elton Dry ABSTRACT: An improved process for dewaxing petroleum oil stocks. A dual solvent consisting of an autorefrigerant and a wax antisolvent is employed to chill the petroleum oil and precipitate out the wax. The autorefrigerant is used to strip the wax antisolvent from both the precipitated wax and the dewaxed oil and may be used additionally as blow gas for the filters.

Wax mduc I Dewaxed Oil P/aduv! LOW-POUR DEWAXING PROCESS UTILIZING DUAL SOLVENTS BACKGROUND OF THE INVENTION This invention relates to a process for dewaxing normally liquid hydrocarbon fractions. More particularly, it relates to a process for dewaxing lubricating oils utilin'ng a dual solvent, consisting of an autorefrigerant type solvent and a wax antisolvent.

DESCRIPTION OF THE PRIOR ART Two types of crude oil are normally utilized in the manufacture of lube and specialty oils; namely, paraffinic crudes and naphthenic crudes. Parafiinic crudes are generally used in the production of high quality motor oils, aviation oils, turbine oils, and hydraulic oils. The paraffinic crudes produce lubricating oils with a relatively high viscosity index. However, these crudes contain waxy constituents which must be removed in in order to confer satisfactory pour point and cloud point on the oil. It is essential to reduce the pour point of the oil so that it will flow under all conditions of use, including starting up a cold engine. In recent years there has been an increased demand for lube oils having relatively low pour points, at or below F. Low-cloud points, which generally go along with low-pour points, are required to gain customer acceptance of the oil although cloud point is not usually a critical performance characteristic of the oil.

Various processes for dewaxing petroleum lubricating oil stocks are known in the art. Generally in these processes the waxy oil is mixed with a solvent at a temperature sufficient to effect thorough solution of the oil in the solvent. The extent of dilution employed is usually dependent upon the particular oil and the particular solvent employed, and is usually adjusted to facilitate easy handling and optimum filtration rates. The waxy mixture is then chilled in order to precipitate wax particles or crystals from the solution, and these crystals are then separated from the dewaxed oil.

Two types of solvent dewaxing processes have gained widespread use in the art. These are known as the ketonedewaxing process and the propane dewaxing process, respectively.

Mixtures of methyl ethyl ketone and higher homologues, or of methyl ethyl ketone with benzene or toluene are generally used as the dewaxing solvent in the ketone-dewaxing process. With solvents of this type, chilling is accomplished in indirect, scraped surface heat exchange with the cold filtrate resulting from the process, and with a refrigerant such as propane, propylene or ammonia.

Another dewaxing process in commercial use employs a normally gaseous hydrocarbon such as propane as the solvent. The propane is added to the warm waxy oil under pressure, as a liquid. Pressure is then gradually reduced, allowing a portion of the normally gaseous hydrocarbon to vaporize, thereby chilling the oil and causing the wax to crystallize out of solution. In such a procedure the normally gaseous hydrocarbon is referred to as an autorefrigerant.

The chilled solution containing the precipitated wax particles is then sent to a device for separating the solid from the liquid phase. Continuous, rotary drum filters are normally used for this purpose.

Practical advantages for the propane process are (I) use of autorefrigeration, (2) ease of solvent recovery, and (3) generally higher filter rates. Disadvantages as compared with conventional ketone plants are (l) the need for higher pressure filters, and (2) the difficulty in reaching low-pour point, as compared to the ketone process.

The propane-dewaxing process is at a disadvantage in reaching lowpour points as compared with the ketone process because of the relatively high solubility of wax in the propane solvent. This necessitates chilling to a lower temperature with propane in order to reduce the wax solubility to a given level and hence make dewaxed oil of a given pour point. With propane or propylene as the dewaxing solvent, the filtration temperature may be some 30 to 50 below the desired pour point, whereas with ketone solvents this temperature difference is generally less than 25 F., and may be as low as 5 to 10 F.

Dewaxing has been improved in recent years by the use of a dual-solvent system. Basically, this technique employs a highly volatile autorefrigerant, such as propane or propylene, in admixture with a solvent, such as a ketone, which reduces wax solubility. This added component is tenned a wax antisolvent." Such technique is disclosed, for example, in the copending U.S. Pat. application of J. Walker, Ser. No. 656,697, filed July 28, 1967 now US. Pat. No. 3,503,870. The dual-solvent system combines most of the advantages of the propane and the ketone dewaxing process. Low-pour points, with small temperature differences between filtration temperature and pour point, can be attained in the dual solvent process. At the same time, autorefrigeration may be used. and the necessity for scraped surface heat exchangers is eliminated. Although the dual solvent system has many advantages, the search has continued for an efficient solvent recovery process in which the solvents are separated efficiently from the oil and the wax with minimal loss of solvent by occlusion in the wax and oil.

SUMMARY OF THE INVENTION It has been discovered according to this invention that substantially complete separation of the wax antisolvent from the dewaxed oil and the wax can be achieved by stripping the wax and the dewaxed oil separately with the autorefrigerant vapors. The autorefrigerant can also be used as a blow gas in the filters to loosen the wax cakes from the filter cloth.

It is an object of this invention to provide an improved method for dewaxing a wax-containing hydrocarbon fraction.

It is a further object of this invention to provide an improved method of recovering the dewaxed oil and wax in' a dewaxing process employing a dual-solvent system.

It is a further object of this invention to separate the wax antisolvent from the dewaxed oil and the wax in a dewaxing process utilizing an autorefrigerant and a wax antisolvent.

It is yet another object of this invention to provide a dual solvent dewaxing process with a reduced solvent circulation rate.

In accordance with this invention, these and other objects are accomplished by using an autorefrigerant to strip the wax antisolvent from a mixture of wax antisolvent and a dewaxed hydrocarbon oil or wax. In addition, the autorefrigerant may then also be used as blowback gas in the filters which separate the wax from the dewaxed oil. Additionally, by utilizing the same material twice, first as stripping agent and then as blow gas before recovery, total load on the compressor for solvent circulation is reduced.

BRIEF DESCRIPTION OF THE DRAWING The sole FIGURE if a flow diagram of the dewaxing process.

DETAILED DESCRIPTION Referring to the drawing, a hot petroleum distillate fraction is fed from the oil storage tank 1 through line 2 and mixed with preheated dual solvent, introduced from storage drum 3 through line 4 and preheater 5a. This dual solvent consists of a wax antisolvent and an autorefrigerant.

Conditions in the storage tank and the solvent preheater 5a are adjusted so that the oil-solvent mixture is not enough to dissolve any wax crystals present. The solution is then cooled in cooler 5b until it temperature approaches the cloud point and sent to a warm-solution surge drum 5c.

The oil-solvent mixture is then fed through either line 6a or 6b into a batch chiller, 7a or 7b, and is cooled by vaporizing at least a portion of the autorefrigerant. Where more than one batch chiller is being employed, while a batch of feed-solvent mixture is being chilled in one chiller, the other is being emptied, warmed up, and recharged. As a batch is being chilled, the autorefrigerant vapors leave the chiller, 7a or? b, overhead through line 9a or 9b, thereby gradually decreasing the pressure within the chiller. The initial pressure is about 90 to 200 p.s.i.a. and the final pressure is about 10 to 40 p.s.i.a. The final temperature in the chiller is about to 50 F. It is often advantageous to introduce additional chilled dual solvent into the chiller, 7a or 7b, simultaneously with the vaporization of autorefrigerant. Dual solvent may thus be introduced from storage drum 3 via line 90 or 9d into chiller 7a or 7b. This additional solvent may be chilled prior to entry into the chiller by indirect heat exchange with cold filtrate or wax slurry in heat exchanger 57 in order to recover refrigeration. It is necessary that the temperature of this solvent as it mixes with the contents of the chiller is substantially the same as that of the slurry present therein at any given time, in order to avoid shock chilling. This is done by providing a contacting zone in the vapor space of the chiller, or spraying the makeup solvent in through a spray header so that the entering solvent is heat exchanged by direct contact with the autorefrigeration vapor leaving the chiller.

This chilliiig operation results in the crystallization of at least a portion of the wax in the petroleum fraction. The waxdewaxed oil-solvent mixture is then withdrawn from the chiller7a or 7b bottom through line a or 10b, and fed to filter feed drum 1 1. An overhead vent line 1 la is provided for venting autorefrigerant vapors from filter feed drum 1 l.

The proportions of autorefrigerant and of wax antisolvent in the dual-solvent mixture after autorefrigeration to filtering temperature generally range from about 65 to 90 percent by volume of autorefrigerant, and conversely about 10 to 35 percent by volume of antisolvent, based on the total liquid volume of the dual solvent mixture. Preferred proportions are from about 75 to 85 percent by volume of autorefrigerant and about to percent of antisolvent.

The solvent to oil ratio at the filtration temperature may vary from about one to four parts by volume of dual-solvent mixture per volume of waxy oil. Preferred operations use a solvent to oil mixture of about 1.5 to 3 parts by volume of solvent per volume of oil.

Since significant portion of the autorefrigerant is vaporized in the batch-chilling operations, the solvent composition and the dilution ratio may change during batch chilling. The initial dilution ratio and the proportion of autorefrigerant in the solvent may both be higher than the values quoted in the preceding paragraphs for conditions at filtration temperature. The extent of this change depends upon the degree of cooling done by autorefrigeration, the initial dilution ratio, and how much makeup solvent is added during chilling as described hereinafter.

The chilled waxy slurry, which contains precipitated wax, dewaxed oil, wax antisolvent, and unvaporized autorefrigerant, passes from filter feed drum 11 through line 12 into filter 13 in which the liquid phase is separated from the solid or waxy phase. The temperature of the wax-oil mixture in filter 13 is generally in the range of 0 to -50 F., and is approximately 10 to F. below the pour point of the final dewaxed oil. Filter 13 may be a conventional rotary drum filter. Other means, such as a centrifuge for separating the waxy solid residue from the liquid phase may be used instead of filter 13, if desired.

A waxy filter cake forms on the filter cloth of filter 13, and a filtrate containing dewaxed oil, antisolvent, and unvaporized autorefrigerant is also obtained. The waxy filter cake is washed with cold solvent introduced from solvent storage rum 3 via line to remove additional dewaxed oil. This solvent is preferably cooled in heat exchanger 45a prior to its introduction to filter 13. A blow gas, which may be vaporized autorefrigerant, may be used as required to remove wax from the filter cloth. This blow gas is introduced to the filter 13 via lie 38. The filter may be hot washed with antisolvent introduced through lines 39 and 40 when needed, in order to clear the filter cloth. This becomes necessary whenever the filter cloth becomes fouled, as is evidenced by a drop in filter rate.

The washed filter cake may be reslurried with enough cold solvent to permit it to flow through line 42 to wax surge drum 43. Simultaneously, filtrate consisting of dewaxed oil, wax antisolvent, and unvaporized autorefrigerant is removed from the filter 13 via line 14, and is passed to filtrate drum l5. Filtrate drum 15 will have an overhead line 16 for venting any gas which is carried over in the dewaxed oil, thus maintaining the desired difi'erential pressure across the filter drum.

The overhead lines 9a, 9b, 11a and 16, all of which convey vapors consisting essentially of autorefrigerant, merge in a single line 17. The autorefrigerant in line 17 is introduced to the inlet end of a compressor 18. This compressor is preferably a multistage compressor having an interstage takeoff 18a as well as a high-pressure takeoff 18b. Autorefrigerant taken off at the interstage takeoff 18a is used to strip solvent from wax and from dewaxed oil, as will be explained later. The pressure at this interstage takeoff is generally in the range of 25 to p.s.i.g. Additional autorefrigerant is taken off at high-pressure takeoff 18b and is returned via vapor line 19, condenser 20, and line 21 to the solvent storage drum 3. Vapors of the wax antisolvent are admixed with the autorefrigerant in line 19 and condensed with the autorefrigerant in condenser 20 as will be explained in more detail hereinafter.

Solvent recovery systems are essentially the same for both the filtrate and the wax streams. The bulk of the solvent in these streams is recovered by a high-pressure flash, operated at from to 250 p.s.i.g., and from 275 to 450 F. These high-pressure flashes are carried out in drum 23 for the filtrate and drum 25 for the wax, with no particular attempt to segregate the two-solvent components. The flashed solvent vapors flow to condenser 20 via lines 24, 26 and 27, and thence to solvent storage drum 3, not requiring any recompression. Dewaxed oil containing some remaining solvent, chiefly the wax antisolvent component, is withdrawn from flash tower 23 and conveyed to stripping tower 31 via line 33. Similarly, wax containing some oil and remaining solvent is conveyed from flash tower 25 to stripping tower 32 via line 35.

Nearly all of the remaining wax antisolvent is then separated from both the wax and the dewaxed oil by contacting these streams with autorefrigerant vapors, and this is accomplished by passing these vapors in the towers countercurrently to the dewaxed oil-wax streams in intermediate pressure-stripping towers 31 and 32, maintained at from 275 to 450 F. These autorefrigerant vapors normally containing only a small amount of antisolvent, typically 0.5 to 2.0 percent by weight, and are thus satisfactory for stripping most of the antisolvent from the oil and wax.

The intermediate pressure-stripping towers 31 and 32, in which autorefrigerant vapors are countercurrently contacted with a dewaxed hydrocarbon fraction are maintained at from between 20 to 50 p.s.i.g., and contacting is preferably carried out at a rate of from 2 to 10 pounds of vapor per barrel of solvent-free product of hydrocarbon oil or wax.

The overhead streams from these two towers, which comprise mixtures of autorefrigerant and wax antisolvent vapors, are conveyed through lines 36 and 34 to solvent splitter 37, which may be a conventional distillation column. This column serves several purposes. It segregates enough of the solvent components in substantially pure fonn to permit rapid adjustment of the ratio of the two in the total circulating solvent when desired. Additionally, it provides a supply of segregated wax antisolvent which is stored in surge drum 55 and may be used occasionally, as required, to hot wash filter 13 via lines 39 and 40 and heater 56. It also provides a stream of essentially pure autorefrigerant vapors at a pressure suitable for use, via line 38, as blowback to loosen the wax cake on filter 13. Thus, these autorefrigerant vapors are used twice, for each circulation through the compressor, thereby enhancing the efficiency of the process. Any excess of the segregated wax antisolvent may be returned to solvent storage drum 3 via lines 41 and 21.

The dewaxed oil stream from intermediate pressure stripper 31 passes through line 46 into low-pressure flash tower 47, operated at from 0 to 20 p.s.i.g., and from 275 to 450 F.,

where a small amount of residual solvent may be removed therefrom. Similarly, the wax stream from intermediate pressure stripper 32 passes through line 54 into low-pressure flash tower 48 operated at from O to 20 p.s.i.g., and from 275 to 450 F., where some additional solvent may also be removed. The additional solvent thus recovered may be recycled through lines 51, 52 and 53. Final dewaxed oil and wax products are withdrawn through lines 49 and 50, respectively.

The dewaxed oil and wax products made in this process may be sold as such or may be subjected to further conventional processing, such as hydrofining for example. In addition, it is further contemplated that the initial waxy oil feed may be either a raw petroleum fraction or may have previously been subjected to solvent extraction with a suitable solvent such as phenol, furfural, nitrobenzene, propane or other well-known solvents for extraction and/or deasphalting, as well as other procedures such as hydrotreating.

1n carrying out the process of this invention, a dewaxing aid or crystal modifier may be used if desired, such as is commonly employed in propane dewaxing. These dewaxing aids are generally polymeric materials or condensation products, a commonly used one being a condensation product of wax and naphthalene. When present in trace amounts during crystal formation, this material modifies crystal growth, improving the filterability of the resultant slurry.

The petroleum fractions employed in this process may be either distillate or residual stocks. Typical distillates will have an initial boiling point of at least 550 F. Both distillate and residual stocks requiring dewaxing will typically have a wax content of from about to about 25 weight percent, a pour point between about 80 and 120 F., and a cloud point between about 90 and 130 F. These feedstocks may come from any wax-containing crude. Suitable sources include the following crudes: Arabian, Kuwait, Panhandle, North Louisiana, Tia Juana Medium, Western Canada, Midcontinent, etc.

The wax antisolvents used in conjunction with this invention are substances which decrease the solubility of the wax in the oil-solvent mixture, thereby causing the wax crystals to precipitate out at a higher temperature, and thereby reducing the spread between the filtration temperature and the final pour point of the oil. Those used herein will be ketones boiling higher than the autorefrigerant, such as methyl ethyl ketone, methyl propyl ketones, methyl butyl ketones, and acetone. The most preferred wax antisolvent is acetone.

The autorefrigerants employed in conjunction with this invention are liquified normally gaseous hydrocarbons from C to C such as propane, propylene, ethane, ethylene, butanes, butylenes, and mixtures thereof. Propylene is the preferred autorefrigerant. The invention will be more apparent from the preferred embodiment and working examples set forth below.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawing, a petroleum oil fraction boiling between 700 and l,l00 F., containing between and percent wax, having an initial pour point of between 90 and 120 F., and an initial cloud point between 95 and 125 F., is fed from the heated oil storage tank 1 through line 2 and mixed with the preheated dual solvent, propylene and acetone, to give a mix temperature between 120 and 140 F. to ensure complete solution of wax, and is then cooled in cooler 5b to about the cloud point (initial wax-crystallization point) of the mixture. The propylene-acetone solvent mixture from storage drum 3 comprises about 87.5 percent propylene and 2.5 percent acetone by liquid volume, and is stored in the drum as a liquid at about 100 F. and 200 p.s.i.g. The mixture of feed and dual solvent from heater 5a and cooler 5b is charged alternately to batch chillers 7a and 7b.

While the chilling process is being carried out in one batch chiller the chilled contents of the other chiller are transferred to filter feed drum 11, the emptied chiller is warmed up, preferably by pressuring with hot gas, which may be obtained from the compressor outlet. The chiller is then refilled with another charge of the warm feed-solvent mixture. Chilling of a single batch in chiller 7a will be described.

The chiller is shut off after filling about one-half full, allowing room for expansion due to boil up during chilling. To accomplish the chilling, vapors are drawn off at a controlled rate through line 9a. As the pressure in the chiller is lowered, more solvent evaporates, thereby chilling the remaining mixture. As the pressure is thus lowered from about 200 p.s.i.g. to about 5 p.s.i.g., the composition of the vapor leaving the chiller ranges from 0.7. to 1.5 weight percent acetone, the remainder being propylene. The composition of the liquid solvent in the chiller varies from about 12.5 percent acetone-87.5 percent propylene by liquid volume at the start of chilling (60 F.) to approximately 20 percent acetonepercent propylene by liquid volume at the end of chilling. Also, cooled makeup solvent is added to chiller 7a through line 9c during the chilling to replace the material evaporated. The makeup solvent is introduced at 31 18 F., but is wanned up to about the temperature of the slurry at any given time, this being accomplished by countercurrent contacting of the makeup stream with the vapors leaving chiller 7a. This may be done by use of contacting devices such as trays in the upper portion of the chiller, or by spraying the makeup solvent into the chiller in the form of fine droplets. If makeup solvent is not used, a higher solvent to oil dilution ratio must be used at the start of chilling to arrive at the same dilution for filtration; the evaporative chilling load will be somewhat higher and the change in solvent composition during chilling also somewhat higher.

After the completion of chilling, the cold slurry is transferred from chiller7 a via line 10a to filter feed drum 1 1, from which it is fed through line 12 to filter 13.

Filter 13 is a conventional continuous horizontal rotary drum filter of the type presently employed in commercial propane dewaxing plants. Filtration temperature is substantially the same as the final chilling temperature, about -30 F. in order to obtain a final dewaxed oil product of 0 F. pour point. As the filter drum, partially submerged in the slurry, rotates, liquid is forced through the filter cloth and is withdrawn through line 14 to filtrate rundown drum 15 while a layer of wax cake builds up on the cloth. After the wax cake emerges from the slurry, the continuing difierential pressure between the outside and inside of the drum causes vapors, and also solvent which may be applied to the cake by spray headers, to be drawn through the cake, thereby reducing its oil content and adding to the filtrate. At an appropriate point on the downhill side of the filter, blowback gas is applied to loosen the wax cake from the cloth. The cake falls into a trough where it is slurried with additional solvent for transfer through line 42 to wax surge drum 43. The blow gas used on the filter comprises approximately 99 percent propylene, and is obtained from solvent splitter 37 through line 38. This same propylene had been used previously in intermediate-pressure strippers 31 and 32.

In filtrate rundown drum l5, maintained at about 30 F. and from 0 to about 10 p.s.i.g., the vapor and liquid phases are separated. The vapors (approximately 99 percent propylene) pass overhead in line 16 and are added to the gas stream of similar composition coming from chiller 7a or 7b, i.e., in line 17.

For solvent recovery the liquid from filtrate rundown drum 15 is pumped through a heater to high-pressure flash drum 23 which operates at from 300 to 350 F. and from 200 to 235 p.s.i.g. Under these conditions approximately 96 percent of the propylene is vaporized and 88 percent of the acetone, leaving only about 3 to 5 weight percent acetone and 3 to 4 weight percent propylene dissolved in the oil.

The wax slurry is handled in similar fashion in high-pressure flash drum 2 5, with similar results.

The liquid from high-pressure flash drum 23 is flashed through line 33 to intermediate pressure stripper 31 where it is stripped with propylene gas containing only about 0.5. to 2 weight percent acetone. at 395 F. The overhead gas from dewaxed oil intermediate-pressure stripper 31 is combined with the overhead from the similar intermediate-pressure stripper for wax, 32, and conveyed by lines 34 and 36 to solvent splitter 37. Solvent splitter 37 is a conventional distillation column having at least four theoretical contacting stages or plates, together with heating means at the bottom and a cooling means at the top to establish reflux. The overhead stream is propylene containing about 2 to 4 weight percent acetone, while the bottoms is approximately 99 weight percent acetone. The total solvent content of the bottoms from intermediate-pressure stripper 31 is only about 0.5 weight percent, most of which is propylene. This is further reduced, to about 0.2 weight percent total solvent, in low-pressure flash drum 47. Similarly, the wax stream as bottoms from intermediate pressure stripper 32 is further lowered in solvent content in low-pressure flash drum 48. The dewaxed oil and wax products from drums 47 and 48, respectively, may be further purified by means known in the art. The overhead from the low-pressure flash drums is conveyed via lines 51, 52 and 53 to compressor 18.

EXAMPLE 1 A phenol-extracted petroleum distillate fraction of Arabian light crude having a boiling range of 850 To l,050 F. (equivalent atmospheric temperature), a viscosity of 76 S.S.U./ 210 F., and an initial pour point of greater than 110 F. is fed alternately into two batch-chilling vessels at an overall rate of 6210 barrels per day (b./d.) afier being mixed with 12,420 b./d. of dual solvent, i.e. propylene and acetone. The dual solvent comprises 12.5 percent acetone and 87.5 percent propylene by liquid volume. Batches of diluted feed are chilled by releasing vapor at a controlled rate to reduce the system pressure and evaporate solvent, while makeup solvent is added to maintain a constant dilution ratio. However, due to preferential evaporation of the propylene component, the solvent composition changes from 12.5 percent to about 20 percent acetone by liquid volume while cooling the mixture by autorefrigeration from 80 F. to -20 F. The cooling results in the crystallization of about 16 weight percent of wax from the feedstock. The resulting slurry is filtered on a continuous rotary filter at 20 F. to separate the wax and produce an oil of +l F. pour point. Solvent is recovered from both the filtrate and the wax streams separately in three successive stages, as follows:

1. Flash at 300 F. and 235 p.s.i.g., recovering a out 90 percent of the total solvent without need to recompress the propylene;

2. Strip at an intermediate pressure of 35 p.s.i.g. and a somewhat higher temperature of 400 F. with 4 to 1bs./bbl. of about 99 percent purity propylene vapor, taken interstage from the compressor, thereby increasing the total recovery of acetone to about 99.8 percent and of propylene to about 99.6 percent; and

3. Flash at 5 p.s.i.g. and same temperature to recover additional propylene and acetone.

The overhead from step 2 is quenched and fractionated to provide a gas stream consisting largely of propylene for use as blow gas on the filter and a liquid stream of approximately 99 percent acetone which is used in part for periodic hot washing of the filter cloth and in part returned directly to solvent storage.

What is claimed is:

1. In a process for dewaxing a wax-containing liquid hydrocarbon fraction by contacting said hydrocarbon fraction with a dual solvent comprising an autorefrigerant and a wax antisolvent, vaporizing at least a portion of the autorefrigerant so that at least a portion of the wax is precipitated from the hydrocarbon fraction filtering the hydrocarbon fraction so that the precipitated wax is separated from the hydrocarbon fraction, separating the autorefrigerant from the precipitated wax and from the hydrocarbon fraction, separating the wax antisolvent from the precipitated wax and from the hydrocarbon fraction, and recovering a hydrocarbon fraction aving a lower pour point, the improvement which comprises separating the wax antisolvent from the precipitated wax and the hydrocarbon fraction by stripping the wax antisolvent therefrom utilizing autorefrigerant in the vapor phase as stripping gas.

2. The process of claim 1 wherein the stripping of wax antisolvent from the hydrocarbon fraction is carried out at a temperature of from between 275 to 450 F.

3. The process of claim 1 wherein the stripping of wax antisolvent from precipitated wax is carried out at a temperature of from between 275 to 450 F.

4. The process of claim 2-wherein the autorefrigerant vapor, at from between 275 to 450 F., and from between 20 to 50 p.s.i.g., is contacted with the hydrocarbon fraction at a rate of from between 2 to 10 lbs. of vapor/bbl. of solvent-free product of hydrocarbon oil.

5. The process of claim 3 wherein the autorefrigerant vapor, at from between 275 F. to 450 F., and from between 20 to 50 p.s.i.g., is contacted with the precipitated wax at a rate of from between 2 to 10 lbs. of vapor/bbl. of solvent-free product wax.

6. The process of claim 1 wherein the autorefrigerant comprises a normally gaseous hydrocarbon, from C to C 7. The process of claim 1 wherein the autorefrigerant is selected from the group consisting of propane, propylene, ethane, ethylene, butanes, butylenes, and mixtures thereof.

8. The process of claim 1 wherein the autorefrigerant consists essentially of propylene.

9. The process of claim 1 wherein the wax antisolvent is selected from the group consisting of methyl ethyl ketone, methyl propyl ketones, methyl butyl ketones, and mixtures thereof. 1

10. The process of claim 1 wherein the wax antisolvent consists essentially of acetone.

11. In a process for dewaxing a wax-containing liquid hydrocarbon fraction by contacting said hydrocarbon fraction with a dual solvent comprising an autorefrigerant and a wax antisolvent, vaporizing at least a portion of the autorefrigerant so that at least a portion of the wax is precipitated from the hydrocarbon fraction, filtering the hydrocarbon fraction so that the precipitated wax is separated from the hydrocarbon fraction, separating the autorefrigerant from the precipitated wax and from the hydrocarbon fraction, separating the wax antisolvent from the precipitated wax and from the hydrocarbon fraction, and recovering a hydrocarbon fraction having a lower pour point, the improvement which comprises separating the wax antisolvent from the precipitated wax and the hydrocarbon fraction by stripping the wax antisolvent therefrom utilizing autorefrigerant in the vapor phase as stripping gas, separating the stripper overheads into an autorefrigerant rich gas and an antisolvent rich liquid in a solvent splitter, using the overhead gas from the solvent splitter as blow gas on the filters and using the heated splitter bottoms to wash the filters to remove small particles of wax from the filter cloth.

12. The process of claim 11 wherein the autorefrigerant comprises propylene and the wax antisolvent comprises acetone.

i I k 

2. The process of claim 1 wherein the stripping of wax antisolvent from the hydrocarbon fraction is carried out at a temperature of from between 275* to 450* F.
 3. ThE process of claim 1 wherein the stripping of wax antisolvent from precipitated wax is carried out at a temperature of from between 275* to 450* F.
 4. The process of claim 2 wherein the autorefrigerant vapor, at from between 275* to 450* F., and from between 20 to 50 p.s.i.g., is contacted with the hydrocarbon fraction at a rate of from between 2 to 10 pounds of vapor/bbl. of solvent-free product of hydrocarbon oil.
 5. The process of claim 3 wherein the autorefrigerant vapor, at from between 275* to 450* F., and from between 20 to 50 p.s.i.g., is contacted with the precipitated wax at a rate of from between 2 to 10 lbs. of vapor/bbl. of solvent-free product wax.
 6. The process of claim 1 wherein the autorefrigerant comprises a normally gaseous hydrocarbon, from C2 to C4.
 7. The process of claim 1 wherein the autorefrigerant is selected from the group consisting of propane, propylene, ethane, ethylene, butanes, butylenes, and mixtures thereof.
 8. The process of claim 1 wherein the autorefrigerant consists essentially of propylene.
 9. The process of claim 1 wherein the wax antisolvent is selected from the group consisting of methyl ethyl ketone, methyl propyl ketones, methyl butyl ketones, and mixtures thereof.
 10. The process of claim 1 wherein the wax antisolvent consists essentially of acetone.
 11. In a process for dewaxing a wax-containing liquid hydrocarbon fraction by contacting said hydrocarbon fraction with a dual solvent comprising an autorefrigerant and a wax antisolvent, vaporizing at least a portion of the autorefrigerant so that at least a portion of the wax is precipitated from the hydrocarbon fraction, filtering the hydrocarbon fraction so that the precipitated wax is separated from the hydrocarbon fraction, separating the autorefrigerant from the precipitated wax and from the hydrocarbon fraction, separating the wax antisolvent from the precipitated wax and from the hydrocarbon fraction, and recovering a hydrocarbon fraction having a lower pour point, the improvement which comprises separating the wax antisolvent from the precipitated wax and the hydrocarbon fraction by stripping the wax antisolvent therefrom utilizing autorefrigerant in the vapor phase as stripping gas, separating the stripper overheads into an autorefrigerant rich gas and an antisolvent rich liquid in a solvent splitter, using the overhead gas from the solvent splitter as blow gas on the filters, and using the heated splitter bottoms to wash the filters to remove small particles of wax from the filter cloth.
 12. The process of claim 11 wherein the autorefrigerant comprises propylene and the wax antisolvent comprises acetone. 